1. Field of the Invention
The present invention relates to a slitter for paper making. More specifically, the invention relates to a slitter holder having a slitter blade support rod.
2. Description of the Prior Art
In the slitter of this type, in general, the lower blade is secured in the axial direction and the upper blade is brought into lap-contact with the lower blade via a spring to slit paper or any other sheet-like materials. When the slitter is not in operation, the upper blade is separated away from the lower blade and is located at an upper side position with respect to the lower blade. When the slitter is in operation, the upper blade is moved relative to the lower blade and is brought into lap-contact therewith. A slitter holder that is capable of reliably controlling the movement of the upper blade relative to the lower blade has already been proposed as disclosed, for example, in Japanese Utility Model Publication No. 17394/1984 that was filed by the applicant of the present invention. Such a conventional slitter holder is shown in the accompanying FIG. 3.
With reference to a partial section view of FIG. 3, the conventional slitter holder is provided with a fixed mounting fitting 1 that is fixed to a support frame (not diagramed) which holds the slitter holder. The fixed mounting fitting 1 is a hollow member whose upper and lower ends are closed by an upper cover 2 and a lower cover 3 thereby to define a cylinder space 4 therein. An upper blade support rod 5 is provided so as to penetrate through the cylinder space 4. At the lower end of the upper blade support rod 5 is provided an annular member 7 which forms another cylinder space 6. Both ends of the annular member 7 is closed by end plates 8 and 9. In the cylinder space 6 is provided a piston 10 which has a shaft 11 that extends to the outside of the cylinder space 6. To the other end of the shaft 11 is detachably attached a knife holder 20 to which a dish-type knife 24 is fitted by a compression spring 25. The thus fitted dish-type knife 24 is rotated about the shaft 11 by an upper blade drive device (not shown).
To the upper blade support rod 5 is fastened a piston 19 that moves in the cylinder space 4. The piston 19 is upwardly urged at all times by an urging spring 41. The upper blade support rod 5 moves up and down accompanying the piston 19 that moves up and down in the cylinder space 4. Further, the piston 10 that moves in the cylinder space 6 is leftwardly urged in FIG. 3 at all times by an urging spring 44. An adjust screw 45 screwed into the end plate 9 limits the rightward movement of the piston 10 and, hence, limits the movement with respect to the upper blade 24 and the lower blade 40. Drive systems for the pistons 19 and 10 will now be described. The upper end of the cylinder space 4 is connected to a source of air pressure through a passage 2B formed in the upper cover 2, air conduit 46, first delay valve 47 and air conduit 48, and the left end of the cylinder space 6 is connected to the source of air pressure via a passage 7A formed in the annular member 7, passage 5A formed in the rod 5, air conduit 49, second delay valve 50 and air conduit 51. When not energized, the first delay valve 47 and the second delay valve 50 permit the air conduit 46 and 49 to open to the atmosphere, respectively. Therefore, the pistons 19 and 10 are urged upwardly and leftwardly, respectively, by the force of the urging springs 41 and 44. Under this condition, the upper blade 24 is separated away from the lower blade 40 as shown. In operating the slitter, if now the first and second delay valves 47 and 50 are energized, their conditions are switched so that the air conduits 46 and 49 are communicated with the source of air pressure via the air conduits 48 and 51, respectively. The air feeding rate of the first delay valve 47 has been set to be greater by a predetermined value than the air feeding rate of the second delay valve 50. Therefore, the pneumatic pressure is, first, applied to the cylinder space 4 so that the piston 19 moves downwards against the force of the urging spring 41. Namely, the upper blade 24 moves downwards and, then, the pneumatic pressure is applied to the cylinder space 6 whereby the piston 10 moves toward the right against the force of the urging spring 44. The upper blade 24, the,, moves toward the right and, accordingly, the upper blade 24 comes into engagement with the lower blade 40 by a lapping amount determined by the nut 42. To release the engagement between the upper blade 24 and the lower blade 40, the first delay valve 47 and the second delay valve 50 should be de-energized to change over their conditions. At this moment, the air conduits 46 and 49 are opened to the atmosphere, and the pneumatic pressures in the cylinder spaces 4 and 6 are released to the open air. In this case, since the air release rate of the first delay valve 47 has been set to be greater than the air release rate of the second delay valve 50, the piston, first, starts to return toward the left and after the upper blade 24 is separated from the lower blade 40, the piston returns upwards.
According to the conventional slitter holder mentioned above, the upper blade moves downwards and then moves sideways being controlled reliably. Therefore, the upper blade and the lower blade are brought into lap-contact at all times; i.e., the upper blade and the lower blade do not come into collision with one another and are not broken. With the above-mentioned conventional slitter holder, however, a through hole 31 is formed in the lower cover 3 through which the upper blade support rod 5 penetrates and slides, and a dust seal 3A made of rubber is simply provided along the inner circumference of the through hole 31. A slight gap exists between the inner circumferential wall of the through hole 31 and the outer circumferential wall of the upper blade support rod 5 which, at this position, is supported by the tip of the dust seal 3A made of rubber. Therefore, the upper blade support rod 5 is not reliably held at the position of the through hole 31 and rattles. When the slitter is in operation, therefore, the upper blade support rod 5 tends to vibrate in the right and left directions to adversely affect the operation of the slitter. Vibration of the upper blade support rod 5 increases with the increase in the operation speed of the slitter, and the slitter operation is adversely affected more seriously.
An object of the present invention is to provide a slitter holder which is capable of eliminating the aforementioned problem inherent in the conventional slitter holder.